Initiating rebuild actions from ds processing unit errors

ABSTRACT

A method begins by detecting a recovery error when decoding a seemingly valid threshold number of existing encoded data slice. The method continues by sending a notice of the recovery error and a known integrity check value for the data segment to a rebuild module. The method continues by the rebuild module retrieving the set of existing encoded data slices and selectively decoding a different combination of a decode threshold number of existing encoded data slices of the set of existing encoded data slices until the data segment is successfully recovered. The method continues by dispersed storage error encoding the successfully recovered data segment to produce a set of new encoded data slices. The method continues by comparing the seemingly valid encoded data slices with corresponding new encoded data slices on an encoded data slice by encoded data slice basis to identify a corrupted encoded data slice.

CROSS REFERENCE TO RELATED PATENTS

The present U.S. Utility patent application claims priority pursuant to35 U.S.C. §119(e) to U.S. Provisional Application No. 62/260,743,entitled “COMMUNICATING DISPERSED STORAGE NETWORK STORAGE UNIT TASKEXECUTION STATUS”, filed Nov. 30, 2015, which is hereby incorporatedherein by reference in its entirety and made part of the present U.S.Utility patent application for all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

Not applicable.

BACKGROUND OF THE INVENTION

Technical Field of the Invention

This invention relates generally to computer networks and moreparticularly to dispersing error encoded data.

Description of Related Art

Computing devices are known to communicate data, process data, and/orstore data. Such computing devices range from wireless smart phones,laptops, tablets, personal computers (PC), work stations, and video gamedevices, to data centers that support millions of web searches, stocktrades, or on-line purchases every day. In general, a computing deviceincludes a central processing unit (CPU), a memory system, userinput/output interfaces, peripheral device interfaces, and aninterconnecting bus structure.

As is further known, a computer may effectively extend its CPU by using“cloud computing” to perform one or more computing functions (e.g., aservice, an application, an algorithm, an arithmetic logic function,etc.) on behalf of the computer. Further, for large services,applications, and/or functions, cloud computing may be performed bymultiple cloud computing resources in a distributed manner to improvethe response time for completion of the service, application, and/orfunction. For example, Hadoop is an open source software framework thatsupports distributed applications enabling application execution bythousands of computers.

In addition to cloud computing, a computer may use “cloud storage” aspart of its memory system. As is known, cloud storage enables a user,via its computer, to store files, applications, etc. on an Internetstorage system. The Internet storage system may include a RAID(redundant array of independent disks) system and/or a dispersed storagesystem that uses an error correction scheme to encode data for storage.

For cloud storage systems, security is an on-going challenge. Breachprevention and breach detection are two primary issues for secure cloudstorage operation. Breach prevention is directed towards preventingunauthorized access to the cloud storage system. Breach detection isdirected towards detecting a potential unauthorized access, determiningwhen it is unauthorized, and, if it is, taking corrective measures. Suchcorrective measures includes updating breach detection, removinghardware from the system, attempting to recover compromised data, etc.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 is a schematic block diagram of an embodiment of a dispersed ordistributed storage network (DSN) in accordance with the presentinvention;

FIG. 2 is a schematic block diagram of an embodiment of a computing corein accordance with the present invention;

FIG. 3 is a schematic block diagram of an example of dispersed storageerror encoding of data in accordance with the present invention;

FIG. 4 is a schematic block diagram of a generic example of an errorencoding function in accordance with the present invention;

FIG. 5 is a schematic block diagram of a specific example of an errorencoding function in accordance with the present invention;

FIG. 6 is a schematic block diagram of an example of a slice name of anencoded data slice (EDS) in accordance with the present invention;

FIG. 7 is a schematic block diagram of an example of dispersed storageerror decoding of data in accordance with the present invention;

FIG. 8 is a schematic block diagram of a generic example of an errordecoding function in accordance with the present invention;

FIG. 9 is a schematic block diagram of another example of dispersedstorage error encoding of data in accordance with the present invention;

FIG. 10 is a schematic block diagram of another specific example of anerror encoding function in accordance with the present invention;

FIG. 11 is a schematic block diagram of an example of generating slicenames and integrity check values for a set of encoded data slices inaccordance with the present invention;

FIG. 12 is a schematic block diagram of an example of retrieving a setof encoded data slices in accordance with the present invention;

FIG. 13 is a schematic block diagram of an example of creating a new setof encoded data slices from a recovered data segment without error inaccordance with the present invention;

FIG. 14 is a schematic block diagram of an example of comparing a newset of encoded data slices and a retrieved set of encoded data slices inaccordance with the present invention; and

FIG. 15 is a logic diagram of an example of a method of detecting arecovery error in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic block diagram of an embodiment of a dispersed, ordistributed, storage network (DSN) 10 that includes a plurality ofcomputing devices 12-16, a managing unit 18, an integrity processingunit 20, and a DSN memory 22. The components of the DSN 10 are coupledto a network 24, which may include one or more wireless and/or wirelined communication systems; one or more non-public intranet systemsand/or public internet systems; and/or one or more local area networks(LAN) and/or wide area networks (WAN).

The DSN memory 22 includes a plurality of storage units 36 that may belocated at geographically different sites (e.g., one in Chicago, one inMilwaukee, etc.), at a common site, or a combination thereof. Forexample, if the DSN memory 22 includes eight storage units 36, eachstorage unit is located at a different site. As another example, if theDSN memory 22 includes eight storage units 36, all eight storage unitsare located at the same site. As yet another example, if the DSN memory22 includes eight storage units 36, a first pair of storage units are ata first common site, a second pair of storage units are at a secondcommon site, a third pair of storage units are at a third common site,and a fourth pair of storage units are at a fourth common site. Notethat a DSN memory 22 may include more or less than eight storage units36. Further note that each storage unit 36 includes a computing core (asshown in FIG. 2, or components thereof) and a plurality of memorydevices for storing dispersed error encoded data.

Each of the computing devices 12-16, the managing unit 18, and theintegrity processing unit 20 include a computing core 26, which includesnetwork interfaces 30-33. Computing devices 12-16 may each be a portablecomputing device and/or a fixed computing device. A portable computingdevice may be a social networking device, a gaming device, a cell phone,a smart phone, a digital assistant, a digital music player, a digitalvideo player, a laptop computer, a handheld computer, a tablet, a videogame controller, and/or any other portable device that includes acomputing core. A fixed computing device may be a computer (PC), acomputer server, a cable set-top box, a satellite receiver, a televisionset, a printer, a fax machine, home entertainment equipment, a videogame console, and/or any type of home or office computing equipment.Note that each of the managing unit 18 and the integrity processing unit20 may be separate computing devices, may be a common computing device,and/or may be integrated into one or more of the computing devices 12-16and/or into one or more of the storage units 36.

Each interface 30, 32, and 33 includes software and hardware to supportone or more communication links via the network 24 indirectly and/ordirectly. For example, interface 30 supports a communication link (e.g.,wired, wireless, direct, via a LAN, via the network 24, etc.) betweencomputing devices 14 and 16. As another example, interface 32 supportscommunication links (e.g., a wired connection, a wireless connection, aLAN connection, and/or any other type of connection to/from the network24) between computing devices 12 and 16 and the DSN memory 22. As yetanother example, interface 33 supports a communication link for each ofthe managing unit 18 and the integrity processing unit 20 to the network24.

Computing devices 12 and 16 include a dispersed storage (DS) clientmodule 34, which enables the computing device to dispersed storage errorencode and decode data (e.g., data 40) as subsequently described withreference to one or more of FIGS. 3-8. In this example embodiment,computing device 16 functions as a dispersed storage processing agentfor computing device 14. In this role, computing device 16 dispersedstorage error encodes and decodes data on behalf of computing device 14.With the use of dispersed storage error encoding and decoding, the DSN10 is tolerant of a significant number of storage unit failures (thenumber of failures is based on parameters of the dispersed storage errorencoding function) without loss of data and without the need for aredundant or backup copies of the data. Further, the DSN 10 stores datafor an indefinite period of time without data loss and in a securemanner (e.g., the system is very resistant to unauthorized attempts ataccessing the data).

In operation, the managing unit 18 performs DS management services. Forexample, the managing unit 18 establishes distributed data storageparameters (e.g., vault creation, distributed storage parameters,security parameters, billing information, user profile information,etc.) for computing devices 12-14 individually or as part of a group ofuser devices. As a specific example, the managing unit 18 coordinatescreation of a vault (e.g., a virtual memory block associated with aportion of an overall namespace of the DSN) within the DSN memory 22 fora user device, a group of devices, or for public access and establishesper vault dispersed storage (DS) error encoding parameters for a vault.The managing unit 18 facilitates storage of DS error encoding parametersfor each vault by updating registry information of the DSN 10, where theregistry information may be stored in the DSN memory 22, a computingdevice 12-16, the managing unit 18, and/or the integrity processing unit20.

The managing unit 18 creates and stores user profile information (e.g.,an access control list (ACL)) in local memory and/or within memory ofthe DSN memory 22. The user profile information includes authenticationinformation, permissions, and/or the security parameters. The securityparameters may include encryption/decryption scheme, one or moreencryption keys, key generation scheme, and/or data encoding/decodingscheme.

The managing unit 18 creates billing information for a particular user,a user group, a vault access, public vault access, etc. For instance,the managing unit 18 tracks the number of times a user accesses anon-public vault and/or public vaults, which can be used to generate aper-access billing information. In another instance, the managing unit18 tracks the amount of data stored and/or retrieved by a user deviceand/or a user group, which can be used to generate a per-data-amountbilling information.

As another example, the managing unit 18 performs network operations,network administration, and/or network maintenance. Network operationsincludes authenticating user data allocation requests (e.g., read and/orwrite requests), managing creation of vaults, establishingauthentication credentials for user devices, adding/deleting components(e.g., user devices, storage units, and/or computing devices with a DSclient module 34) to/from the DSN 10, and/or establishing authenticationcredentials for the storage units 36. Network administration includesmonitoring devices and/or units for failures, maintaining vaultinformation, determining device and/or unit activation status,determining device and/or unit loading, and/or determining any othersystem level operation that affects the performance level of the DSN 10.Network maintenance includes facilitating replacing, upgrading,repairing, and/or expanding a device and/or unit of the DSN 10.

The integrity processing unit 20 performs rebuilding of ‘bad’ or missingencoded data slices. At a high level, the integrity processing unit 20performs rebuilding by periodically attempting to retrieve/list encodeddata slices, and/or slice names of the encoded data slices, from the DSNmemory 22. For retrieved encoded slices, they are checked for errors dueto data corruption, outdated version, etc. If a slice includes an error,it is flagged as a ‘bad’ slice. For encoded data slices that were notreceived and/or not listed, they are flagged as missing slices. Badand/or missing slices are subsequently rebuilt using other retrievedencoded data slices that are deemed to be good slices to produce rebuiltslices. The rebuilt slices are stored in the DSN memory 22.

FIG. 2 is a schematic block diagram of an embodiment of a computing core26 that includes a processing module 50, a memory controller 52, mainmemory 54, a video graphics processing unit 55, an input/output (I/O)controller 56, a peripheral component interconnect (PCI) interface 58,an IO interface module 60, at least one IO device interface module 62, aread only memory (ROM) basic input output system (BIOS) 64, and one ormore memory interface modules. The one or more memory interfacemodule(s) includes one or more of a universal serial bus (USB) interfacemodule 66, a host bus adapter (HBA) interface module 68, a networkinterface module 70, a flash interface module 72, a hard drive interfacemodule 74, and a DSN interface module 76.

The DSN interface module 76 functions to mimic a conventional operatingsystem (OS) file system interface (e.g., network file system (NFS),flash file system (FFS), disk file system (DFS), file transfer protocol(FTP), web-based distributed authoring and versioning (WebDAV), etc.)and/or a block memory interface (e.g., small computer system interface(SCSI), internet small computer system interface (iSCSI), etc.). The DSNinterface module 76 and/or the network interface module 70 may functionas one or more of the interface 30-33 of FIG. 1. Note that the IO deviceinterface module 62 and/or the memory interface modules 66-76 may becollectively or individually referred to as IO ports.

FIG. 3 is a schematic block diagram of an example of dispersed storageerror encoding of data. When a computing device 12 or 16 has data tostore it disperse storage error encodes the data in accordance with adispersed storage error encoding process based on dispersed storageerror encoding parameters. The dispersed storage error encodingparameters include an encoding function (e.g., information dispersalalgorithm, Reed-Solomon, Cauchy Reed-Solomon, systematic encoding,non-systematic encoding, on-line codes, etc.), a data segmentingprotocol (e.g., data segment size, fixed, variable, etc.), and per datasegment encoding values. The per data segment encoding values include atotal, or pillar width, number (T) of encoded data slices per encodingof a data segment (i.e., in a set of encoded data slices); a decodethreshold number (D) of encoded data slices of a set of encoded dataslices that are needed to recover the data segment; a read thresholdnumber (R) of encoded data slices to indicate a number of encoded dataslices per set to be read from storage for decoding of the data segment;and/or a write threshold number (W) to indicate a number of encoded dataslices per set that must be accurately stored before the encoded datasegment is deemed to have been properly stored. The dispersed storageerror encoding parameters may further include slicing information (e.g.,the number of encoded data slices that will be created for each datasegment) and/or slice security information (e.g., per encoded data sliceencryption, compression, integrity checksum, etc.).

In the present example, Cauchy Reed-Solomon has been selected as theencoding function (a generic example is shown in FIG. 4 and a specificexample is shown in FIG. 5); the data segmenting protocol is to dividethe data object into fixed sized data segments; and the per data segmentencoding values include: a pillar width of 5, a decode threshold of 3, aread threshold of 4, and a write threshold of 4. In accordance with thedata segmenting protocol, the computing device 12 or 16 divides the data(e.g., a file (e.g., text, video, audio, etc.), a data object, or otherdata arrangement) into a plurality of fixed sized data segments (e.g., 1through Y of a fixed size in range of Kilo-bytes to Tera-bytes or more).The number of data segments created is dependent of the size of the dataand the data segmenting protocol.

The computing device 12 or 16 then disperse storage error encodes a datasegment using the selected encoding function (e.g., Cauchy Reed-Solomon)to produce a set of encoded data slices. FIG. 4 illustrates a genericCauchy Reed-Solomon encoding function, which includes an encoding matrix(EM), a data matrix (DM), and a coded matrix (CM). The size of theencoding matrix (EM) is dependent on the pillar width number (T) and thedecode threshold number (D) of selected per data segment encodingvalues. To produce the data matrix (DM), the data segment is dividedinto a plurality of data blocks and the data blocks are arranged into Dnumber of rows with Z data blocks per row. Note that Z is a function ofthe number of data blocks created from the data segment and the decodethreshold number (D). The coded matrix is produced by matrix multiplyingthe data matrix by the encoding matrix.

FIG. 5 illustrates a specific example of Cauchy Reed-Solomon encodingwith a pillar number (T) of five and decode threshold number of three.In this example, a first data segment is divided into twelve data blocks(D1-D12). The coded matrix includes five rows of coded data blocks,where the first row of X11-X14 corresponds to a first encoded data slice(EDS 1_1), the second row of X21-X24 corresponds to a second encodeddata slice (EDS 2_1), the third row of X31-X34 corresponds to a thirdencoded data slice (EDS 3_1), the fourth row of X41-X44 corresponds to afourth encoded data slice (EDS 4_1), and the fifth row of X51-X54corresponds to a fifth encoded data slice (EDS 5_1). Note that thesecond number of the EDS designation corresponds to the data segmentnumber.

Returning to the discussion of FIG. 3, the computing device also createsa slice name (SN) for each encoded data slice (EDS) in the set ofencoded data slices. A typical format for a slice name 80 is shown inFIG. 6. As shown, the slice name (SN) 80 includes a pillar number of theencoded data slice (e.g., one of 1-T), a data segment number (e.g., oneof 1-Y), a vault identifier (ID), a data object identifier (ID), and mayfurther include revision level information of the encoded data slices.The slice name functions as, at least part of, a DSN address for theencoded data slice for storage and retrieval from the DSN memory 22.

As a result of encoding, the computing device 12 or 16 produces aplurality of sets of encoded data slices, which are provided with theirrespective slice names to the storage units for storage. As shown, thefirst set of encoded data slices includes EDS 1_1 through EDS 5_1 andthe first set of slice names includes SN 1_1 through SN 5_1 and the lastset of encoded data slices includes EDS 1_Y through EDS 5_Y and the lastset of slice names includes SN 1_Y through SN 5_Y.

FIG. 7 is a schematic block diagram of an example of dispersed storageerror decoding of a data object that was dispersed storage error encodedand stored in the example of FIG. 4. In this example, the computingdevice 12 or 16 retrieves from the storage units at least the decodethreshold number of encoded data slices per data segment. As a specificexample, the computing device retrieves a read threshold number ofencoded data slices.

To recover a data segment from a decode threshold number of encoded dataslices, the computing device uses a decoding function as shown in FIG.8. As shown, the decoding function is essentially an inverse of theencoding function of FIG. 4. The coded matrix includes a decodethreshold number of rows (e.g., three in this example) and the decodingmatrix in an inversion of the encoding matrix that includes thecorresponding rows of the coded matrix. For example, if the coded matrixincludes rows 1, 2, and 4, the encoding matrix is reduced to rows 1, 2,and 4, and then inverted to produce the decoding matrix.

FIG. 9 is a schematic block diagram of another example of dispersedstorage error encoding of data. In accordance with the data segmentingprotocol, the computing device 12 or 16 divides the data (e.g., a file(e.g., text, video, audio, etc.), a data object, or other dataarrangement) into a plurality of data segments. The number (Y) of datasegments created is dependent of the size of the data and the datasegmenting protocol.

The computing device then computes an integrity check value for eachdata segment 1-Y. In one example, the integrity check value is generatedby performing a hash function on the data segment. As another example,the ICV is generated using a cyclic redundancy check (CRC) function onthe data segment. The integrity check values are then stored locally inthe computing device or in one or more storage units that do not storean encoded data slice associated with the data segment that correspondsto a corresponding ICV. The computing device then appends each integritycheck value to a corresponding data segment (e.g., DS1-DSY).

FIG. 10 illustrates a specific example of Cauchy Reed-Solomon encodingwith a pillar number (T) of five and decode threshold number of three.In this example, a first data segment is divided into twelve data blocks(D1-D12) and 3 ICV blocks (icv1-icv3).

The computing device 12 or 16 then disperse storage error encodes thedata segment using the selected encoding function (e.g., CauchyReed-Solomon) to produce a set of encoded data slices (e.g., EDS1_1_1_1_a1 through EDS 5_1_1_1_a1).

FIG. 11 is a schematic block diagram of an example of generating slicenames and integrity check values for a set of encoded data slices. Foreach encoded data slice, a slice name and integrity check value isgenerated. In particular, five EDSs and SNs are created for this set:1_1_1_1_a1; 2_1_1_1_a1; 3_1_1_1_a1; 4_1_1_1_a1; and 5_1_1_1_a1. Thefirst digit of the EDS and SN represents the slice number in the set(e.g., 1-5); The second digit represents the segment number (e.g., 1-Y);the third digit represents the vault number (e.g., a logical storagecontainer of the DSN having one or more user devices affiliated withit); The fourth digit represents the current revision number of the EDS;The fifth value (e.g., a1) represents a data object identifier.

Continuing with the example, for each encoded data slice (EDS) and/orslice name (SN) of the set, an integrity check value is created. As aspecific example, an ICV is generated from the encoded data slice, theslice name, or both the encoded data slice and the slice name. Forinstance, ICV 1_1_1_1_a1 is created for EDS 1_1_1_1_a1 and/or SN1_1_1_1_a1. The set of encoded data slices, along with correspondingslice names and integrity check values are sent to a set of storageunits for storage.

FIG. 12 is a schematic block diagram of an example of retrieving a setof encoded data slices. As shown, encoded data slices EDS 1_1_1_1_a1through EDS 5_1_1_1_a1 are stored in storage units SU #1-5 withcorresponding slices names (e.g., SN 1_1_1_1_a1-5_1_1_1_a1) andintegrity check values (e.g., ICV 1_1_1_1_a1-5_1_1_1_a1). As is furthershown, “EDS” 3_1_1_1_a1 is a seemingly valid encoded data slice as theslice name and ICV associated with EDS appear to be valid (e.g., a slicelevel ICV (e.g., ICV 3_1_1_1_a1) matches a stored value). However,during a decoding of the seemingly valid encoded data slices, acomputing device detects a recovery error (e.g., the segment level ICV(e.g., ICV for DS1 of FIG. 10) does not match a stored segment levelICV) associated with the data segment. The computing device then sends anotice of the recovery error and a known ICV for the data segment to arebuild module of the DSN.

The rebuilding module retrieves the set of encoded data slices (e.g.,EDS 1_1_1_1_a1-EDS 5_1_1_1_a1) and selectively decodes differentcombinations of a decode threshold number of the encoded data slicesuntil a data segment associated with the set of encoded data slices hasbeen successfully recovered. As a specific example, a decode thresholdis 3 and a pillar width is 5. The rebuild module selects EDS 1_1_1_1_a1,EDS 2_1_1_1_a1, and EDS 3_1_1_1_a1 as the first combination of thedecode threshold number of encoded data slices. The rebuild module thendecodes the first combination to recover a first data segment andcompares the data segment integrity check value (e.g., ICV for DS1 ofFIG. 10) with the known integrity check value. When the comparing isunfavorable (e.g., the data segment ICV is not substantially identicalto a known ICV), the rebuild module selects a second combination of thedecode threshold number of encoded data slices (e.g., EDS 1_1_1_1_a1,EDS 2_1_1_1_a1, and EDS 4_1_1_1_a1). The rebuild module then decodes thesecond combination to produce a second data segment and compares thedata segment integrity check value with the known ICV. In this instance,the comparing is favorable, indicating the data segment has beenrecovered without an error.

FIG. 13 is a schematic block diagram of creating a new set of encodeddata slices from a recovered data segment without error. As shown, therebuilding device computes an integrity check value (ICV) for therecovered data segment without error. The ICV is then appended to therecovered data segment. Then, similar to FIG. 10, the computing devicedispersed storage error encodes the recovered data segment to produce anew set of encoded data slices and a corresponding set of slice names(SN). In this example, the computing device further generates anintegrity check value (ICV) for each encoded data slice (EDS). The ICVmay be created in a variety of ways. For example, the ICV is generatedusing a hash function. As another example, the ICV is generated using acyclic redundancy check (CRC) function.

FIG. 14 is a schematic block diagram of an example of comparing a newset of encoded data slices and a retrieved set of encoded data slices(e.g., the seemingly valid threshold number of existing encoded dataslices). The rebuild module having generated the new set of encoded dataslices, compares the new set of encoded data slices to the retrieved setof encoded data slices to reveal which encoded data slices have beencompromised. For example, the rebuild module identifies EDS 3_1_1_1_a1as a corrupted encoded data slice after comparing EDS 3_1_1_1_a1 with“EDS” 3_1_1_1_a1 and determining that “EDS” 3_1_1_1_a1 is notsubstantially identical to EDS 3_1_1_1_a1. Having identified thecorrupted encoded data slices, the rebuild module sends EDS 3_1_1_1_a1from the new set of encoded data slices to a storage unit to replace thecorrupted “EDS” 3_1_1_1_a1. Alternatively, the rebuild module sends EDS3_1_1_1_a1 to one or more other storage units for storage (e.g., whenthe compromised EDS indicates a security issue, when the compromisedindicates a reliability issue, etc.).

FIG. 15 is a logic diagram of an example of a method of detecting arecovery error. The method begins with step 100, where a computingdevice of a dispersed storage network (DSN) detects a recovery errorwhen decoding a seemingly valid threshold number of existing encodeddata slices of a set of existing encoded data slices. For example, thecomputing device the detects the recovery error by comparing anintegrity check value of a successfully recovered data segment with alocally stored integrity check value of the data segment and when thecomparing yields an unfavorable result, the computing device indicatesthe recovery error. Note the data segment of a data object was dispersedstorage error encoded to produce the set of existing encoded dataslices.

The method continues with step 102, where the computing device sends anotice of the recovery error and a known integrity check value for thedata segment to a rebuild module of the DSN. The method continues withstep 104, where the rebuilding module retrieves the set of existingencoded data slices. Note the computing device may also send pillarnumbers of the seemingly valid threshold number of existing encoded dataslices to the rebuilding module. The method continues with step 106,where the rebuilding module selectively decodes a different combinationof a decode threshold number of existing encoded data slices of the setof existing encoded data slices until the data segment is successfullyrecovered.

The method continues with step 108, where the rebuilding moduledetermines if the integrity check value of the successfully recovereddata segment is valid. For example, for a first combination of the setof existing encoded data slices the rebuilding module recovers a firstdata segment, generates an integrity check value for the first datasegment, compares the integrity check value for the first data segmentwith the known integrity check value, and when the comparing isfavorable, indicates the first combination produces the successfullyrecovered data segment.

When the comparing the integrity check value is unfavorable, the methodloops back to step 106. For example, when the comparing is unfavorable,the rebuild module selects a second combination of the set of existingencoded data slices to produce a second recovered data segment,generates a second integrity check value for the second recovered datasegment, and compares the second integrity check value with the knownintegrity check value. When the comparing is favorable, the rebuildmodule indicates the second combination produces the successfullyrecovered data segment. Note if all combinations of a decode thresholdnumber of existing encoded data slices do not produce a favorablecomparing, the rebuild module may end the method and send an errormessage to the computing device.

When the comparing the integrity check value is favorable, the methodcontinues with step 110, where the rebuild module dispersed storageerror encodes the successfully recovered data segment to produce a setof new encoded data slices. The method continues with step 112, wherethe rebuild module compares the seemingly valid threshold number ofexisting encoded data slices with corresponding new encoded data slicesof the set of new encoded data slices on an encoded data slice byencoded data slice basis to identify a corrupted encoded data slice ofthe seemingly valid threshold number of existing encoded data slices.

For example, for a first existing encoded data slice of the seeminglyvalid threshold number of existing encoded data slices, the rebuildmodule compares a first existing slice name of the first existingencoded data slice with a first new slice name of a first new encodeddata slice of the set of new encoded data slices, compares a firstexisting integrity check value of the first existing encoded data slicewith a first new integrity check value of the first new encoded dataslice and compares a first existing encoded portion of the firstexisting encoded data slice with a first new encoded portion of thefirst new encoded data slice. When one or more of the comparisons isunfavorable, the rebuild module identifies the first existing encodeddata slice as the corrupted encoded data slice. The method continueswith step 114, where the rebuild module sends a new EDS to a storageunit to replace the corrupted encoded data slice. Alternatively, therebuild module also sends one or more of the first new slice name andthe first new integrity check value.

It is noted that terminologies as may be used herein such as bit stream,stream, signal sequence, etc. (or their equivalents) have been usedinterchangeably to describe digital information whose contentcorresponds to any of a number of desired types (e.g., data, video,speech, audio, etc. any of which may generally be referred to as‘data’).

As may be used herein, the terms “substantially” and “approximately”provides an industry-accepted tolerance for its corresponding termand/or relativity between items. Such an industry-accepted toleranceranges from less than one percent to fifty percent and corresponds to,but is not limited to, component values, integrated circuit processvariations, temperature variations, rise and fall times, and/or thermalnoise. Such relativity between items ranges from a difference of a fewpercent to magnitude differences. As may also be used herein, theterm(s) “configured to”, “operably coupled to”, “coupled to”, and/or“coupling” includes direct coupling between items and/or indirectcoupling between items via an intervening item (e.g., an item includes,but is not limited to, a component, an element, a circuit, and/or amodule) where, for an example of indirect coupling, the intervening itemdoes not modify the information of a signal but may adjust its currentlevel, voltage level, and/or power level. As may further be used herein,inferred coupling (i.e., where one element is coupled to another elementby inference) includes direct and indirect coupling between two items inthe same manner as “coupled to”. As may even further be used herein, theterm “configured to”, “operable to”, “coupled to”, or “operably coupledto” indicates that an item includes one or more of power connections,input(s), output(s), etc., to perform, when activated, one or more itscorresponding functions and may further include inferred coupling to oneor more other items. As may still further be used herein, the term“associated with”, includes direct and/or indirect coupling of separateitems and/or one item being embedded within another item.

As may be used herein, the term “compares favorably”, indicates that acomparison between two or more items, signals, etc., provides a desiredrelationship. For example, when the desired relationship is that signal1 has a greater magnitude than signal 2, a favorable comparison may beachieved when the magnitude of signal 1 is greater than that of signal 2or when the magnitude of signal 2 is less than that of signal 1. As maybe used herein, the term “compares unfavorably”, indicates that acomparison between two or more items, signals, etc., fails to providethe desired relationship.

As may also be used herein, the terms “processing module”, “processingcircuit”, “processor”, and/or “processing unit” may be a singleprocessing device or a plurality of processing devices. Such aprocessing device may be a microprocessor, micro-controller, digitalsignal processor, microcomputer, central processing unit, fieldprogrammable gate array, programmable logic device, state machine, logiccircuitry, analog circuitry, digital circuitry, and/or any device thatmanipulates signals (analog and/or digital) based on hard coding of thecircuitry and/or operational instructions. The processing module,module, processing circuit, and/or processing unit may be, or furtherinclude, memory and/or an integrated memory element, which may be asingle memory device, a plurality of memory devices, and/or embeddedcircuitry of another processing module, module, processing circuit,and/or processing unit. Such a memory device may be a read-only memory,random access memory, volatile memory, non-volatile memory, staticmemory, dynamic memory, flash memory, cache memory, and/or any devicethat stores digital information. Note that if the processing module,module, processing circuit, and/or processing unit includes more thanone processing device, the processing devices may be centrally located(e.g., directly coupled together via a wired and/or wireless busstructure) or may be distributedly located (e.g., cloud computing viaindirect coupling via a local area network and/or a wide area network).Further note that if the processing module, module, processing circuit,and/or processing unit implements one or more of its functions via astate machine, analog circuitry, digital circuitry, and/or logiccircuitry, the memory and/or memory element storing the correspondingoperational instructions may be embedded within, or external to, thecircuitry comprising the state machine, analog circuitry, digitalcircuitry, and/or logic circuitry. Still further note that, the memoryelement may store, and the processing module, module, processingcircuit, and/or processing unit executes, hard coded and/or operationalinstructions corresponding to at least some of the steps and/orfunctions illustrated in one or more of the Figures. Such a memorydevice or memory element can be included in an article of manufacture.

One or more embodiments have been described above with the aid of methodsteps illustrating the performance of specified functions andrelationships thereof. The boundaries and sequence of these functionalbuilding blocks and method steps have been arbitrarily defined hereinfor convenience of description. Alternate boundaries and sequences canbe defined so long as the specified functions and relationships areappropriately performed. Any such alternate boundaries or sequences arethus within the scope and spirit of the claims. Further, the boundariesof these functional building blocks have been arbitrarily defined forconvenience of description. Alternate boundaries could be defined aslong as the certain significant functions are appropriately performed.Similarly, flow diagram blocks may also have been arbitrarily definedherein to illustrate certain significant functionality.

To the extent used, the flow diagram block boundaries and sequence couldhave been defined otherwise and still perform the certain significantfunctionality. Such alternate definitions of both functional buildingblocks and flow diagram blocks and sequences are thus within the scopeand spirit of the claims. One of average skill in the art will alsorecognize that the functional building blocks, and other illustrativeblocks, modules and components herein, can be implemented as illustratedor by discrete components, application specific integrated circuits,processors executing appropriate software and the like or anycombination thereof.

In addition, a flow diagram may include a “start” and/or “continue”indication. The “start” and “continue” indications reflect that thesteps presented can optionally be incorporated in or otherwise used inconjunction with other routines. In this context, “start” indicates thebeginning of the first step presented and may be preceded by otheractivities not specifically shown. Further, the “continue” indicationreflects that the steps presented may be performed multiple times and/ormay be succeeded by other activities not specifically shown. Further,while a flow diagram indicates a particular ordering of steps, otherorderings are likewise possible provided that the principles ofcausality are maintained.

The one or more embodiments are used herein to illustrate one or moreaspects, one or more features, one or more concepts, and/or one or moreexamples. A physical embodiment of an apparatus, an article ofmanufacture, a machine, and/or of a process may include one or more ofthe aspects, features, concepts, examples, etc. described with referenceto one or more of the embodiments discussed herein. Further, from figureto figure, the embodiments may incorporate the same or similarly namedfunctions, steps, modules, etc. that may use the same or differentreference numbers and, as such, the functions, steps, modules, etc. maybe the same or similar functions, steps, modules, etc. or differentones.

Unless specifically stated to the contra, signals to, from, and/orbetween elements in a figure of any of the figures presented herein maybe analog or digital, continuous time or discrete time, and single-endedor differential. For instance, if a signal path is shown as asingle-ended path, it also represents a differential signal path.Similarly, if a signal path is shown as a differential path, it alsorepresents a single-ended signal path. While one or more particulararchitectures are described herein, other architectures can likewise beimplemented that use one or more data buses not expressly shown, directconnectivity between elements, and/or indirect coupling between otherelements as recognized by one of average skill in the art.

The term “module” is used in the description of one or more of theembodiments. A module implements one or more functions via a device suchas a processor or other processing device or other hardware that mayinclude or operate in association with a memory that stores operationalinstructions. A module may operate independently and/or in conjunctionwith software and/or firmware. As also used herein, a module may containone or more sub-modules, each of which may be one or more modules.

As may further be used herein, a computer readable memory includes oneor more memory elements. A memory element may be a separate memorydevice, multiple memory devices, or a set of memory locations within amemory device. Such a memory device may be a read-only memory, randomaccess memory, volatile memory, non-volatile memory, static memory,dynamic memory, flash memory, cache memory, and/or any device thatstores digital information. The memory device may be in a form a solidstate memory, a hard drive memory, cloud memory, thumb drive, servermemory, computing device memory, and/or other physical medium forstoring digital information.

While particular combinations of various functions and features of theone or more embodiments have been expressly described herein, othercombinations of these features and functions are likewise possible. Thepresent disclosure is not limited by the particular examples disclosedherein and expressly incorporates these other combinations.

What is claimed is:
 1. A method comprises: detecting, by a computingdevice of a dispersed storage network (DSN), a recovery error whendecoding a seemingly valid threshold number of existing encoded dataslices of a set of existing encoded data slices, wherein a data segmentof a data object was dispersed storage error encoded to produce the setof existing encoded data slices; sending, by the computing device, anotice of the recovery error and a known integrity check value for thedata segment to a rebuild module of the DSN; retrieving, by the rebuildmodule, the set of existing encoded data slices; selectively decoding,by the rebuild module, a different combination of a decode thresholdnumber of existing encoded data slices of the set of existing encodeddata slices until the data segment is successfully recovered; dispersedstorage error encoding, by the rebuild module, the successfullyrecovered data segment to produce a set of new encoded data slices; andcomparing, by the rebuild module, the seemingly valid threshold numberof existing encoded data slices with corresponding new encoded dataslices of the set of new encoded data slices on an encoded data slice byencoded data slice basis to identify a corrupted encoded data slice ofthe seemingly valid threshold number of existing encoded data slices. 2.The method of claim 1, wherein the sending further comprises: sendingpillar numbers of the seemingly valid threshold number of existingencoded data slices.
 3. The method of claim 1, wherein the detecting therecovery error comprises: comparing an integrity check value of thesuccessfully recovered data segment with a locally stored integritycheck value of the data segment; and when the comparing yields anunfavorable result, indicating the recovery error.
 4. The method ofclaim 1, wherein the selectively decoding further comprises: for a firstcombination of the set of existing encoded data slices, recovering afirst data segment; generating an integrity check value for the firstdata segment; comparing the integrity check value for the first datasegment with the known integrity check value; and when the comparing isfavorable, indicating the first combination produces the successfullyrecovered data segment.
 5. The method of claim 4 further comprises: whenthe comparing is unfavorable, selecting a second combination of the setof existing encoded data slices to produce a second recovered datasegment; generating a second integrity check value for the secondrecovered data segment; comparing the second integrity check value withthe known integrity check value; and when the comparing is favorable,indicating the second combination produces the successfully recovereddata segment.
 6. The method of claim 1, wherein the comparing comprises:for a first existing encoded data slice of the seemingly valid thresholdnumber of existing encoded data slices: comparing a first existing slicename of the first existing encoded data slice with a first new slicename of a first new encoded data slice of the set of new encoded dataslices; comparing a first existing integrity check value of the firstexisting encoded data slice with a first new integrity check value ofthe first new encoded data slice; comparing a first existing encodedportion of the first existing encoded data slice with a first newencoded portion of the first new encoded data slice; and when one ormore of the comparisons is unfavorable, identifying the first existingencoded data slice as the corrupted encoded data slice.
 7. The method ofclaim 1 further comprises: sending a new EDS to a storage unit toreplace the corrupted encoded data slice.
 8. A rebuild module comprises:an interface; memory; and a processing module operably coupled to theinterface and the memory, wherein the processing module is operable to:receive, via the interface and from a computing device of a dispersedstorage network (DSN), a recovery error regarding a seemingly validthreshold number of existing encoded data slices of a set of existingencoded data slices and a known integrity check of a data segment,wherein the data segment of a data object was dispersed storage errorencoded to produce the set of existing encoded data slices; retrieve,via the interface the set of existing encoded data slices from storageunits of the DSN; selectively decode a different combination of a decodethreshold number of existing encoded data slices of the set of existingencoded data slices until the data segment is successfully recovered;dispersed storage error encode the successfully recovered data segmentto produce a set of new encoded data slices; and compare the seeminglyvalid threshold number of existing encoded data slices withcorresponding new encoded data slices of the set of new encoded dataslices on an encoded data slice by encoded data slice to identified acorrupted encoded data slice of the seemingly valid threshold number ofexisting encoded data slices.
 9. The rebuild module of claim 8, whereinthe processing module is further operable to: receive, via theinterface, pillar numbers of the seemingly valid threshold number ofexisting encoded data slices.
 10. The rebuild module of claim 8, whereinthe processing module is further operable to detect the recovery errorby: comparing an integrity check value of the successfully recovereddata segment with a locally stored integrity check value of the datasegment; and when the comparing yields an unfavorable result, indicatethe recovery error.
 11. The rebuild module of claim 8, wherein theprocessing module is further operable to perform the selectivelydecoding by: for a first combination of the set of existing encoded dataslices, recovering a first data segment; generating an integrity checkvalue for the first data segment; comparing the integrity check valuefor the first data segment with the known integrity check value; andwhen the comparing is favorable, indicating the first combinationproduces the successfully recovered data segment.
 12. The rebuild moduleof claim 11, wherein the processing module is further operable to: whenthe comparing is unfavorable, select a second combination of the set ofexisting encoded data slices to produce a second recovered data segment;generate a second integrity check value for the second recovered datasegment; compare the second integrity check value with the knownintegrity check value; and when the comparing is favorable, indicate thesecond combination produces the successfully recovered data segment. 13.The rebuild module of claim 8, wherein the processing module is furtheroperable to: for a first existing encoded data slice of the seeminglyvalid threshold number of existing encoded data slices: compare a firstexisting slice name of the first existing encoded data slice with afirst new slice name of a first new encoded data slice of the set of newencoded data slices; compare a first existing integrity check value ofthe first existing encoded data slice with a first new integrity checkvalue of the first new encoded data slice; compare a first existingencoded portion of the first existing encoded data slice with a firstnew encoded portion of the first new encoded data slice; and when one ormore of the comparisons is unfavorable, identify the first existingencoded data slice as the corrupted encoded data slice.
 14. The rebuildmodule of claim 8, wherein the processing module is further operable to:send, via the interface, a new EDS to a storage unit to replace thecorrupted encoded data slice.